The present invention relates to a new and improved construction of upset head at a high-strength tension wire wherein at the transition between the head and the wire there is formed a seating surface for support purposes, and this invention further pertains to a new and improved method for the production of such head.
It is known for considerable time to provide tension or tensioning wires with upset heads, specifically cold upset heads. The tension wires are supported at one end by means of these heads at an anchoring body. Apart from the diameter of the wire there of course also is of considerable importance the seating surface between the head and the wire. With conventional upset heads, oftentimes possessing a spherical shape, the maximum head diameter, i.e., the largest head diameter is located at a relatively great distance from the seating surface, this being considered in relation to the height of the head. It has been found that this state-of-the-art position of the maximum head diameter in the case of cold upset heads has associated therewith relatively poor material deformation during the shaping operation, which in turn can lead to fissures, even if such are of a fine nature, at the surface and internally of the head. Furthermore, it is to be noted that the cold working or deformation of a material, apart from its metallurgical composition, in the first instance is dependent upon its strength characteristics and structure. In comparison with normal cold upset steels drawn tension wires for prestressed concrete structures possess more than twice as great strength, less contraction rupture and a different structure. The upsetting of anchoring heads therefore requires, both with regard to the shaping or forming thereof as well as also with respect to the actual upset technique, special measures.